Researchers are increasingly focused on two-dimensional materials, and a new study details the superconducting potential of surface-functionalized, out-of-plane ordered double transition-metal MXenes. Mohammad Keivanloo, Fateme Dinmohammad, and Shashi B. Mishra, working with colleagues from the Department of Physics at University of Tehran in collaboration with Binghamton University-SUNY, Yokohama National University, Institut Teknologi Bandung, JAIST, and the Quantum and Nano Technology Research Group, present first-principles calculations examining the electronic structure and electron-phonon coupling within these materials. Their investigation of 128 candidate compounds revealed 32 mechanically, dynamically, and thermodynamically stable structures exhibiting superconductivity with transition temperatures ranging from 0.1 to 52 K, with MoScNO demonstrating the highest transition temperature of 52 K and a 10 meV superconducting gap. This work is significant as it identifies a novel class of 2D materials with potentially high-temperature superconductivity, offering insights into anisotropic behaviour and the role of anharmonicity in determining superconducting properties.
Recent work focuses on surface-functionalized, out-of-plane ordered double transition-metal MXenes (o-MXenes), a relatively unexplored family of materials exhibiting unique structural and electronic properties. These o-MXenes, created by stacking and ordering transition metals, present a novel platform for achieving higher superconducting transition temperatures.
Researchers employed first-principles calculations to systematically investigate a broad range of 128 o-MXene candidates, functionalized with fluorine, oxygen, chlorine, and hydrogen. The study reveals that 32 of these compounds demonstrate mechanical, dynamic, and thermodynamic stability, with predicted superconducting transition temperatures (Tc) ranging from 0.1 K to an impressive 52 K.
Notably, a specific compound, Mo2ScN2O2, stands out, achieving the highest Tc of 52 K alongside a superconducting gap of approximately 10 meV. This gap represents the energy required to break a Cooper pair, the fundamental charge carriers in a superconductor, and is a key indicator of superconducting strength. Further analysis using the anisotropic Eliashberg equation confirms that Mo2ScN2O2 behaves as an anisotropic two-gap superconductor, meaning its superconducting properties differ depending on the direction within the material and it possesses two different energy scales for Cooper pair formation.
Incorporating the effects of anharmonicity, deviations from simple harmonic motion in the atomic lattice, slightly reduces the predicted Tc, but does not eliminate the potential for high-temperature superconductivity. The research also delves into the role of flat bands, electronic states with minimal kinetic energy, in enhancing electron-phonon coupling, a crucial mechanism for superconductivity, and provides detailed analysis of vibrational modes exhibiting anharmonic behaviour.
Computational screening reveals superconducting promise in functionalised double transition-metal MXenes
First-principles calculations underpinned this work, enabling a comprehensive investigation into the superconducting potential of surface-functionalized, out-of-plane ordered double transition-metal MXenes, or o-MXenes. These calculations allowed detailed examination of electronic structure, electron-phonon coupling (EPC, the interaction between electrons and lattice vibrations), anharmonicity, and anisotropy effects on superconductivity.
A broad compositional search was undertaken, systematically evaluating 128 different o-MXene candidates with the general formula M M X T, where M represents transition metals (Mo, W; Sc, Ti, V, Mo, Zr, Nb, Ta) and X is either carbon or nitrogen. These materials were then functionalized with terminating groups including fluorine, oxygen, chlorine, and hydrogen to assess the impact of surface chemistry on their properties.
To determine structural viability, the research team assessed mechanical, dynamic, and thermodynamic stability for each candidate material. Density functional theory was employed to optimise the atomic configurations and calculate phonon dispersion curves, confirming the absence of imaginary frequencies indicative of instability. Following this screening process, 32 compounds were identified as stable, exhibiting predicted superconducting transition temperatures (T ) ranging from 0.1 K to 52 K.
The highest T was observed for the Mo ScN O compound, reaching 52 K, accompanied by a superconducting gap of 10 meV, a crucial parameter defining the energy required to break a Cooper pair. Anisotropic effects on superconductivity were then explored by solving the Eliashberg equation, a fundamental equation in superconductivity theory, which accounts for the directional dependence of electron-phonon interactions.
This revealed that Mo ScN O exhibits anisotropic two-gap superconductivity, meaning that the superconducting energy gap varies depending on the direction of electron momentum. Furthermore, the influence of anharmonicity, deviations from simple harmonic lattice vibrations, was incorporated into the calculations to refine the predicted T values and provide a more realistic assessment of material performance. Analysis of flat-band induced EPC enhancement and the presentation of EPC matrix elements as functions of phonon wavevector q provided insight into the vibrational modes driving superconductivity and their anharmonic behaviour.
Predicted Stability and Superconducting Properties of o-MXene Compounds
Calculations reveal that 32 of 128 examined o-MXene compounds exhibit mechanical, dynamic, and thermodynamic stability, predicting superconducting transition temperatures ranging from 0.1 K to 52 K. The compound Mo2ScN2O2 demonstrates the highest predicted transition temperature of 52 K, accompanied by a superconducting gap of 10 meV. This gap size indicates a robust superconducting state, potentially facilitating higher-current applications.
Analysis employing the anisotropic Eliashberg equation confirms that Mo2ScN2O2 exhibits anisotropic two-gap superconductivity, meaning that the superconducting properties differ depending on the direction within the material. Incorporating anharmonic effects into the calculations resulted in a slight decrease in the transition temperature, though the material remains a strong candidate for high-temperature superconductivity.
Further investigation into electron-phonon coupling revealed enhancement induced by flat bands, highlighting the crucial role of specific vibrational modes in promoting superconductivity. EPC matrix elements were calculated as functions of phonon wavevector q, providing detailed insight into the vibrational behaviour of these materials. The research identifies specific vibrational modes exhibiting anharmonic behaviour, suggesting that these modes play a significant role in determining the superconducting properties.
These anharmonicities, while reducing Tc slightly, do not negate the potential for high-temperature superconductivity in Mo2ScN2O2. The study’s comprehensive analysis of stability, electronic structure, and phonon behaviour provides a detailed understanding of the superconducting mechanisms within this novel class of materials.
The Bigger Picture
The relentless search for room-temperature superconductivity has often focused on complex materials and extreme conditions, but this work suggests a surprisingly accessible pathway lies within the rapidly expanding family of MXenes. These two-dimensional materials, already attracting attention for their diverse properties, are shown to exhibit superconductivity at temperatures up to 52 Kelvin, not quite ambient, but a significant leap forward for this class of compounds.
What makes this notable is not simply the achieved temperature, but the sheer number of promising candidates identified through high-throughput computational screening. For years, materials scientists have been hampered by the slow, painstaking process of synthesizing and testing potential superconductors. This research bypasses much of that bottleneck, leveraging first-principles calculations to predict the superconducting potential of 128 different MXene configurations before a single crystal is grown.
The discovery of multiple stable, superconducting compounds, even with modest transition temperatures, dramatically expands the landscape for targeted experimental work. However, the predicted superconductivity relies heavily on computational models, and the influence of material imperfections, inevitable in real-world synthesis, remains an open question.
The observed anisotropy in the superconducting behaviour of the most promising candidate also requires further investigation; understanding and controlling this directionality could be crucial for device applications. Future efforts will likely focus on refining these calculations with more sophisticated models of electron-phonon interactions, and crucially, on verifying these predictions through rigorous experimental synthesis and characterisation. The potential payoff, efficient energy transmission, levitating trains, and revolutionary computing technologies, justifies the continued pursuit.
👉 More information
🗞 High-Tc Superconductivity in Functionalized Out-of-Plane Ordered Double Transition Metal MXenes
🧠ArXiv: https://arxiv.org/abs/2602.12960